When invasive weeds are removed with herbicides, revegetation of native species is often desirable. The extended soil activity of aminocyclopyrachlor is important for long-term weed control but could reduce recovery of native species as well. The effect of aminocyclopyrachlor applied alone or with chlorsulfuron on cool- and warm-season grass species commonly used for revegetation was evaluated. The cool-season grasses included green needlegrass, intermediate wheatgrass, and western wheatgrass, whereas the warm-season grasses were big bluestem, sideoats grama, and switchgrass. A separate experiment was conducted for each species. Aminocyclopyrachlor was applied at 91 to 329 g ha⁻¹ alone or with chlorsulfuron from 42 to 133 g ha⁻¹ approximately 30 d after emergence. Warm-season grasses generally were more tolerant of aminocyclopyrachlor than the cool-season grasses evaluated in this study. Switchgrass and big bluestem were the most tolerant of the warm-season species when aminocyclopyrachlor was applied at 168 g ha⁻¹ and averaged 199 and 150% forage production, respectively, compared with the control. Green needlegrass was the most tolerant cool-season grass. Western wheatgrass was the least tolerant species evaluated because forage production only averaged 32% of the control the year after treatment and thus would not be suitable for seeding if aminocyclopyrachlor was applied. The effect of chlorsulfuron applied with aminocyclopyrachlor varied by grass species. For example, green needlegrass injury 8 wk after treatment (WAT) averaged 30 and 48% when aminocylopyrachlor was applied alone, respectively, but injury was reduced to less than 16% when aminocyclopyrachlor was applied with chlorsulfuron. However, injury on the less-tolerant intermediate wheatgrass ranged from 48 to 92% by 4 WAT when aminocyclopyrachlor was applied alone and from 60 to 86% when chlorsulfuron was included in the treatment.

Nomenclature: Aminocyclopyrachlor; chlorsulfuron; big bluestem, Andropogon gerardii Vitman; green needlegrass, Nassella viridula (Trin.) Barkworth; intermediate wheatgrass, Thinopyrum intermedium (Host) Barkworth & D. R. Dewey; sideoats grama, Bouteloua curtipendula (Michx.) Torr.; switchgrass, Panicum virgatum L.; western wheatgrass, Pascopyrum smithii (Rydb.) A. Löve.

Management Implications: Land managers often utilize an integrated program to control invasive weed species. Methods can include the use of fire, herbicides, and/or grazing followed by revegetation with native species. However, reseeding previously weed-infested plant communities more often results in failure and return of the invasive weed rather than successful reestablishment of desirable species. Recently restored prairies are especially vulnerable to invasive species because the plant community has not yet become established. Three cool- and three warm-season grass species were evaluated for tolerance to the rangeland and wildland herbicide aminocyclopyrachlor. The herbicide was applied alone and with chlorsulfuron approximately 30 d after seeded grasses emerged. The warm-season grasses (big bluestem, sideoats grama, and switchgrass) generally were more tolerant to aminocyclopyrachlor than the cool-season grasses (green needlegrass, intermediate wheatgrass, and western wheatgrass), with green needlegrass the most tolerant of the cool-season species evaluated. Warm-season grass yield the year after treatment was similar to or exceeded the control as long as aminocyclopyrachlor was applied at 168 g ha⁻¹ or less. Western wheatgrass was the least tolerant grass evaluated; forage production averag